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The storage account has an Azure Resource Manager lock that protects it from accidental deletion. Your storage account has a Read-only lock that prevents any changes or deletions to the resource.
In order to delete the fileshare, you need to remove the lock first and then try to delete the Azure File Share.
Note: You can always create the same lock again to protect your resource from accidental deletion. I recommend that you create the lock again after you delete the fileshare.
The below articles explain more about Resource locking. https://learn.microsoft.com/en-us/azure/storage/common/lock-account-resource?tabs=portal
Protect your Azure resources with a lock - Azure Resource Manager | Microsoft Learn
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